Refrigerant of 1,1-difluoroethylene

ABSTRACT

Refrigerants comprising 1,1-difluoroethylene and one or more hydrofluoroalkanes, in particular difluoromethane (R-32), trifluoromethane (R-23), 1,1-difluoroethane (R-152a), 1,1,1-trifluoroethane (R-143a), 1,1,1,2-tetrafluoroethane (R-134a) and/or pentafluoroethane (R-125).

FIELD OF THE INVENTION

The present invention relates to refrigerants, to refrigerantcompositions containing these refrigerants, and to the use of theserefrigerants in heat transfer equipment, in particular in mechanicalrefrigeration systems.

TECHNOLOGY REVIEW

The invention relates in particular to refrigerants referred to as the"medium and low temperature" type, that is to say refrigerants making itpossible to achieve temperatures of between about -25° C. and -50° C.,which can be used in all fields of medium and low temperaturerefrigeration such as, in particular, commercial refrigeration,refrigerated transport, air conditioning and various industrialprocesses, as well as refrigerants referred to as the "very-lowtemperature" type, that is to say refrigerants making it possible toachieve temperatures of between about -50° C. and -100° C.

In mechanical refrigeration systems, the evaporation of a liquidrefrigerant at low pressure causes heat to be removed from the mediumsurrounding the evaporator. The gas resulting from the evaporation isthen compressed and sent to a condenser where it condenses, giving upthe heat to the medium surrounding the condenser. Finally, thecondensate is returned to the evaporator through a pressure-reliefvalve. Systems of this type are described in Ullmann's Encyclopedia ofIndustrial Chemistry, 5th Ed., 1988, vol. B3, chapter 19, pages 1 to 20.

Chlorodifluoromethane (R-22) or the azeotrope of R-22 withchloropentafluoroethane (R-115), referred to as R-502, areconventionally used in mechanical refrigeration systems of the "mediumand low temperature" type. Chlorotrifluoromethane (R-13),bromotrifluoromethane (R-13B1) or the azeotrope of R-13 withtrifluoromethane (R-23), referred to as R-503, are conventionally usedin "very-low temperature" mechanical refrigeration systems.Chlorofluorocarbons, such as R-13 and R-115, bromofluorocarbons, such asR-13B1, and hydrochlorofluorocarbons, such as R-22, have for a number ofyears been suspected of having detrimental effects on the stratosphericozone layer. Various international agreements stipulate the progressivereduction, or even complete cessation, of their manufacture and theiruse. Further to the possibility of destroying ozone, it has beensuggested that significant concentrations of halogenated refrigerants inthe atmosphere could contribute to the atmospheric warming phenomenon(this phenomenon is referred to as the greenhouse effect). It istherefore desirable to replace existing refrigerants by substituterefrigerants, which do not contain chlorine, thereby having zero ozonedepletion potential (ODP), and which preferably have a relatively shortlifetime in the atmosphere, thereby having a low global warmingpotential (HGWP).

Further to having minimal environmental impact, a substitute refrigerantshould preferably be non-toxic, non-inflammable, chemically stable andnon-corrosive. Furthermore, it should have suitable physical andthermodynamic properties, ideally making it possible to obtain similarefficiency, refrigeration capacity, compressor discharge temperature andcompression ratio to those of the refrigerant which it replaces, as wellas, if possible, a higher pressure in the evaporator than atmosphericpressure, in order to prevent any moisture from entering therefrigeration system.

Certain refrigerants which do not destroy the stratospheric ozone layerhave already been proposed as a replacement for R-22 or R-502. Inparticular, U.S. Pat. No. 5,035,823 has proposed a refrigerantconsisting of 1,1,1-trifluoroethane (R-143a) and1,1,1,2-tetrafluoroethane (R-134a); patent application WO 92/19199 hasproposed a refrigerant consisting of difluoromethane (R-32) and R-134a;patent application WO 92/16597 has proposed a refrigerant consisting oftrifluoromethane (R-23), R-32 and R-134; and U.S. Pat. No. 5,211,867 hasproposed a refrigerant consisting of 1,1,1-trifluoroethane (R-143a) andpentafluoroethane (R-125). However, these refrigerants have somedrawbacks, including a refrigerating capacity which is generally lessthan that of R-22 and/or a relatively high HGWP.

SUMMARY OF THE INVENTION

The object of the present invention is to provide refrigerants whichhave little or no effect on the environment and which have thermodynamicproperties similar to those of R-22 or R-502, allowing them to be usedin existing medium and low temperature refrigeration machines.

A further object of the invention is to provide refrigerants which havelittle or no effect on the environment and which have thermodynamicproperties similar to those of R-13, R-13B1 or R-503, allowing them tobe used in existing very-low temperature refrigeration machines.

To this end, the present invention relates to refrigerants whichessentially consist of 1,1-difluoroethylene (VF2) and at least onehydrofluoroalkane of formula C_(a) H_(b) F_(c), with a an integer equalto 1 or 2, b an integer from 1 to 4 and c an integer from 2 to 5, thesum of b and c being equal to 2a+2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents the curves of boiling temperature and dew temperature ofthe binary VF2 and R-23 compositions at various pressures, as a functionof the percentage by weight of VF2 in the composition. The change in theazeotropic composition as a function of pressure is given by the dashedcurve.

FIG. 2 presents the curves of boiling temperature and dew temperature ofthe binary VF2 and R-125 compositions at various pressures, as afunction of the percentage by weight of VF2 in the composition.

FIG. 3 presents the curves of boiling temperature and dew temperature ofthe binary VF2 and R-32 compositions at various pressures, as a functionof the percentage by weight of VF2 in the composition.

FIG. 4 presents the curves of boiling temperature and dew temperature ofthe binary VF2 and R-143a compositions at various pressures, as afunction of the percentage by weight of VF2 in the composition.

Key for the Figures

FIG. 1 azeotrope (VF2% by weight).

FIG. 2 1.0 bar, 2.0 bar, 5.0 bar, 5.0 bar, 10.0 bar (VF2% by weight).

FIG. 3 1.0 bar, 2.0 bar, 5.0 bar, 7.0 bar, 10.0 bar (VF2% by weight).

FIG. 4 0.5 bar, 1.0 bar, 2.0 bar, 5.0 bar, 10.0 bar (VF2% by weight).

DETAILED DESCRIPTION OF THE INVENTION

The hydrofluoroalkane in the refrigerants according to the invention ispreferably selected from trifluoromethane (R-23), difluoromethane (R32),1,1-difluoroethane (R-152a), 1,1,1-trifluoroethane (R-143a),1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125) andmixtures thereof.

The refrigerants according to the invention may contain from 0.1 to99.9% by weight of VF2 and from 99.9 to 0.1% of hydrofluoroalkane(s).They usually contain at least 1% by weight of VF2. They generallycontain at least 1.5% by weight thereof. They preferably contain atleast 2% by weight thereof. The refrigerants according to the inventionusually contain at most 99% by weight of VF2. They generally contain atmost 90% by weight thereof. They preferably contain at most 80% byweight thereof. It is particularly preferable for them to contain atmost 70% by weight thereof.

By appropriate selection of the hydrofluoroalkane and the proportions oftheir constituents, the refrigerants according to the invention may besuitable for use in machines of the medium and low temperature type, orin machines of the very-low temperature type, as they are defined above.

Those refrigerants according to the invention which are adapted for usein existing medium and low temperature refrigeration machines, hereafterreferred to as refrigerants of the medium and low temperature type,preferably contain at least one hydrofluoroalkane selected fromdifluoromethane (R-32), 1,1-difluoroethane (R-152a),1,1,1-trifluoroethane (R-143a), 1,1,1,2-tetrafluoroethane (R-134a) andpentafluoroethane (R-125).

Refrigerants according to the invention of the medium and lowtemperature type usually contain at least 1% by weight of VF2. Theygenerally contain at least 1.5% by weight thereof. They preferablycontain at least 2% by weight thereof. The refrigerants according to theinvention of medium and low temperature type usually contain at most 40%by weight of VF2. They generally contain at most 35% by weight thereof.They preferably contain at most 30% by weight thereof. It isparticularly preferable for them to contain at most 25% by weightthereof.

Refrigerants according to the invention, of the medium and lowtemperature type, which have given good results essentially consist offrom 65 to 99% by weight of hydrofluoroalkane(s) and from 1 to 35% byweight of VF2. Most often, they essentially consist of from 70 to 98% byweight of hydrofluoroalkane(s) and from 2 to 30% by weight of VF2. Theserefrigerants of medium and low temperature type essentially consist offrom 75 to 97.5% by weight of hydrofluoroalkane(s) and from 2.5 and 25%by weight of VF2. The refrigerants of medium and low temperature typewhich are more particularly preferred consist essentially of from 80 to97.5% by weight of hydrofluoroalkane(s) and 2.5 to 20% by weight of VF2.

In a first, preferred embodiment of the refrigerants of medium and lowtemperature type of the invention, the refrigerants of medium and lowtemperature type essentially consist of

(a) 1,1-difluoroethylene (VF2);

(b) 1,1,1,2-tetrafluoroethane (R-134a) and/or pentafluoroethane (R-125);and optionally

(c) difluoromethane (R-32), 1,1,1-trifluoroethane (R-143a) and/or1,1-difluoroethane (R-152a).

Of these, the refrigerants containing R-134a are particularly preferred.The ternary refrigerants, of medium and low temperature type,VF2/R-134a/R-32 are more particularly preferred.

Further to VF2 in the quantities given above, the refrigerants of thefirst embodiment of the refrigerants of medium and low temperature typeof the invention generally contain at least 15% by weight of R-134aand/or R-125. They preferably contain at least 20% by weight thereof. Itis particularly preferable for them to contain at least 25% by weightthereof. The refrigerants of the first embodiment of the refrigerants ofmedium and low temperature type of the invention usually contain at most99% by weight of R-134a and/or R-125. They generally comprise at most98.5% by weight thereof. They preferably comprise at most 98% by weightthereof. Advantageously, the refrigerants of the first embodiment of therefrigerants of medium and low temperature type of the invention containR-134a and/or R-125 in a quantity such that the refrigerants arenon-flammable.

The refrigerants of the first embodiment of the refrigerants of mediumand low temperature type of the invention may furthermore contain R-32,R-143a and/or R-152a. They usually contain at most 80% by weightthereof. They generally comprise at most 75% by weight thereof. Theypreferably comprise at most 70% by weight thereof.

In a second embodiment of the refrigerants of medium and low temperaturetype of the invention, the refrigerants of medium and low temperaturetype essentially consist of

(a) 1,1-difluoroethylene (VF2);

(b) 1,1-difluoroethane (R-152a); and

(c) difluoromethane (R-32) and/or 1,1,1-trifluoroethane (R-143a).

Further to VF2 in the quantities given above, the refrigerants of thesecond embodiment of the refrigerants of medium and low temperature typeof the invention generally contain at least 35% by weight of R-152a.They preferably comprise of at least 40% by weight thereof. It isparticularly preferable for them to contain at least 50% by weightthereof. The refrigerants of the second embodiment of the refrigerantsof medium and low temperature type of the invention usually comprise atmost 85% by weight of R-152a. They generally comprise at most 80% byweight thereof. They preferably comprise at most 75% by weight thereof.The remainder of the refrigerants of the second embodiment of therefrigerants of medium and low temperature type of the inventionconsists of R-32 and/or R-143a.

The refrigerants according to the invention, of medium and lowtemperature type, find an application in the techniques of producingcooling or heating, such as refrigeration machines and heat pumps of thecompression type. They may in particular replace R-22 or R-502 in theirusual applications. The refrigerants according to the invention, ofmedium and low temperature type, are more particularly suitable forapplications which currently employ R-22. The working conditions for therefrigerants according to the invention, of medium and low temperaturetype, are similar to those for R-22 or R-502, which allows them to beused in compressors which currently employ R-22 or R-502, substantiallywithout modifications.

All other things being equal, the presence of VF2 in the refrigerantsaccording to the invention, of medium and low temperature type, leads,under the working conditions for R-22, to an increase in therefrigeration capacity and the pressure in the evaporator. Furthermore,because of the very low HGWP of VF2 (about 0.004), its presence in therefrigerants according to the invention gives them a low HGWP.

Moreover, the use of the refrigerants according to the invention, ofmedium and low temperature type, leads to a temperature at the end ofcompression which is lower than that obtained with R-22.

Those refrigerants according to the invention which are adapted for usein existing very-low temperature refrigeration machines, hereafterreferred to as refrigerants of the very-low temperature type, preferablycontain at least one hydrofluoroalkane selected from trifluoromethane(R-23), difluoromethane (R-32), 1,1,1-trifluoroethane (R-143a) andpentafluoroethane (R-125). Particularly preferred refrigerants of thevery-low temperature type contain at least one hydrofluoroalkane chosenfrom trifluoromethane (R-23), difluoromethane (R-32) andpentafluoroethane (R-125).

The refrigerants according to the invention, of very-low temperaturetype, usually contain at least 1% by weight of VF2. They generallycontain at least 5% by weight thereof. They preferably contain at least10% by weight thereof. The refrigerants according to the invention, ofvery-low temperature type, usually contain at most 99% by weight of VF2.They generally contain at most 90% by weight thereof. They preferablycontain at most 80% by weight thereof. It is particularly preferable forthem to contain at most 70% by weight thereof.

Refrigerants according to the invention, of very-low temperature type,which have given good results essentially consist of from 10 to 95% byweight of hydrofluoroalkane(s) and from 5 to 90% by weight of VF2. Mostoften, they essentially consist of from 20 to 90% by weight ofhydrofluoroalkane(s) and from 10 to 80% by weight of VF2. Moreparticularly preferred refrigerants of very-low temperature typeessentially consist of from 30 to 75% by weight of hydrofluoroalkane(s)and from 25 to 70% by weight of VF2.

In a first embodiment of the refrigerants of very-low temperature typeof the invention, the refrigerants of very-low temperature typeessentially consist of

(a) 1,1-difluoroethylene (VF2); and

(b) difluoromethane (R-32), 1,1,1-trifluoroethane (R-143a) and/orpentafluoroethane (R-125).

Of these, the refrigerants containing R-32 and/or R-125 are preferred.The refrigerants of very-low temperature type VF2/R-125 andVF2/R-32/R-125 are particularly preferred.

In a second, preferred embodiment of the refrigerants of very-lowtemperature type of the invention, the refrigerants of very-lowtemperature type essentially consist of

(a) 1,1-difluoroethylene (VF2);

(b) trifluoromethane (R-23); and optionally

(c) difluoromethane (R-32), 1,1,1-trifluoroethane (R-143a) and/orpentafluoroethane (R-125).

Of these, the binary refrigerants VF2/R-23 are particularly preferred.

Further to VF2 in the quantities given above, the refrigerants of thesecond embodiment of the refrigerants of very-low temperature type ofthe invention generally contain at least 1% by weight of R-23. Theypreferably comprise at least 5% by weight thereof. It is particularlypreferable for them to contain at least 10% by weight thereof. It ismore particularly preferable for them to contain at least 20% by weightthereof. The refrigerants of the second embodiment of the refrigerantsof very-low temperature type of the invention usually comprise at most99% by weight of R-23. They generally comprise at most 95% by weightthereof. They preferably comprise at most 90% by weight thereof. It isparticularly preferable for them to contain at most 80% by weightthereof.

The refrigerants of the second embodiment of the refrigerants ofvery-low temperature type of the invention may furthermore contain R-32,R-143a and/or R-125. They usually contain at most 80% by weight thereof.They generally comprise at most 70% by weight thereof. They preferablycomprise at most 60% by weight thereof. It is particularly preferablefor them to comprise at most 50% by weight thereof.

Of the refrigerants of the second embodiment of the refrigerants ofvery-low temperature type of the invention, the more particularlypreferred refrigerants are those which contain VF2 and R-23 inproportions in which they form an azeotrope or a pseudo-azeotrope.

Basically, the thermodynamic state of a fluid is defined by fourindependent variables: pressure (P), temperature (T), the composition ofthe liquid phase (X) and the composition of the gas phase (Y). Anazeotrope is a particular system, with at least two components, forwhich, at a given temperature and a given pressure, X is equal to Y. Apseudo-azeotrope is a system, with at least two components, for which,at a given temperature and a given pressure, X is substantially equal toY. In practice, a pseudo-azeotrope behaves almost like a true azeotropeas regards the tendency not to fractionate during boiling orevaporation. Its composition therefore remains substantially constantduring phase changes in the refrigeration cycle, and also in the eventof refrigerant leaking from the refrigeration system. For the purposesof the present invention, the term pseudo-azeotrope will be used todenote a mixture of at least two constituents, the boiling point ofwhich, at a given pressure, differs from the boiling point of theazeotrope by a maximum of 3° C., preferably by a maximum of 1° C.

The binary refrigerants VF2/R-23 containing from 0.1 to 99.9% by weightof VF2 and from 99.9 to 0.1% by weight of R-23 are pseudo-azeotropes.Those containing from 1 to 90% by weight of VF2 and from 99 to 10% byweight of R-23 are preferred. Those containing from 5 to 80% by weightof VF2 and from 95 to 20% by weight of R-23 are particularly preferred.Those containing from 10 to 70% by weight of VF2 and from 90 to 30% byweight of R-23 are more particularly preferred. The most particularlypreferred pseudo-azeotropic binary refrigerants VF2/R-23 contain aboutfrom 35 to 60% by weight of VF2 and from 65 to 40% by weight of R-23.The azeotropic VF2 and R-23 composition varies, within this preferredrange, as a function of pressure (see FIG. 1, dashed line).

The refrigerants according to the invention, of very-low temperaturetype, make it possible to achieve temperatures from -50° C. to about-100° C. They are particularly well-suited for achieving temperaturesranging about from -50 to -90° C. They may therefore be used asrefrigerants in very-low temperature refrigeration systems, inparticular for very-low temperature refrigerators, for refrigerationchambers for quick-freezing foodstuffs, for refrigeration chambers ofscientific laboratories and for large industrial refrigeration plants,in particular as a replacement for R-13, R-13B1 or R-503.

The refrigerants according to the invention are generally used inrefrigerant compositions which comprise, in addition to the refrigerant,one or more additives used conventionally in refrigerant compositions,such as stabilizers or lubricants, the exact nature of which dependsmainly on the intended use of the composition.

The invention therefore also relates to a refrigerant compositioncomprising a refrigerant, according to the invention, as defined above,and at least one additive.

In the refrigerant composition according to the invention, the additivesmust be compatible with the constituents of the refrigerant. Inparticular, they must be chemically inert with respect to theconstituents of the refrigerant at the normal working temperatures forthe composition according to the invention. The nature of the additivesand their proportion in the composition must moreover be chosen so thatthey do not significantly affect the vaporization temperature of therefrigerant. In particular, the additives may be selected fromlubricants, hydrofluoroalkanes and 1,1-difluoroethylene stabilizers, VF2polymerization inhibitors and corrosion inhibitors. Their proportion byweight (the sum of all the additives) does not generally exceed 50% ofthe overall mass of the composition, and preferably does not exceed 25%.In practice, proportions of 0.1 to 20% by weight are recommended. Theproportion of the additives is expressed as % by weight of the totalmass of the refrigerant composition. As a variant, the refrigerantcomposition may comprise one or more refrigerant compounds other thanthe constituents of the refrigerants described above, in particularpropane (R-290).

The invention also relates to the use of the refrigerants and of therefrigerant compositions according to the invention in all types of heattransfer equipment operating using compression. They may be used toproduce cooling by a method involving the condensation of therefrigerant and its subsequent evaporation in a heat exchanger incontact with a body to be refrigerated. They may also be used to produceheating by a method involving evaporation of the refrigerant and itssubsequent condensation in a heat exchanger in contact with a body to beheated.

The invention is illustrated by FIGS. 1 to 4 and by the followingExamples 1 to 5.

FIG. 1 presents the curves of boiling temperature and dew temperature ofthe binary VF2 and R-23 compositions at various pressures, as a functionof the percentage by weight of VF2 in the composition. The change in theazeotropic composition as a function of pressure is given by the dashedcurve.

FIG. 2 presents the curves of boiling temperature and dew temperature ofthe binary VF2 and R-125 compositions at various pressures, as afunction of the percentage by weight of VF2 in the composition.

FIG. 3 presents the curves of boiling temperature and dew temperature ofthe binary VF2 and R-32 compositions at various pressures, as a functionof the percentage by weight of VF2 in the composition.

FIG. 4 presents the curves of boiling temperature and dew temperature ofthe binary VF2 and R-143a compositions at various pressures, as afunction of the percentage by weight of VF2 in the composition.

EXAMPLES Example 1

Using the Peng-Robinson state equation described in IndustrialEngineering Chem. Fund. 1976, (15), p. 59, a thermodynamic performanceanalysis was carried out for several refrigerants according to theinvention, of medium and low temperature type. By way of comparison, thesame analysis was performed for R-134a alone, for R-22 and for variousknown refrigerant mixtures consisting of hydrofluoroalkanes.

The parameters of the refrigeration cycle are characteristic of the useof R-22 as refrigeration fluid. The parameters chosen are a temperatureat the start of evaporation (T_(evap)) of -30° C., a temperature at theend of condensation (T_(cond)) fixed at 30° C., superheating fixed at 10K (temperature difference of 10° C.), subcooling fixed at 5 K(temperature difference of 5° C.) and an isentropic efficiency of thecompressor fixed at 0.8.

The temperature at the end of compression (T_(max)), the pressure in theevaporator (P_(ev)), the compression ratio (R=pressure at thecondenser/pressure at the evaporator), the mechanical coefficient ofperformance (COP) and the volume swept by the compressor (Vol) requiredto obtain a refrigeration power of 10 kW, were estimated.

The value of the temperature at the end of compression is useful forassessing the feasibility of using the refrigerating fluid, it beingpossible for an excessively high temperature to lead to degradation ofthe oil and/or refrigerant which are used, as well as the structuralmaterials of the refrigeration system.

The evaporation pressure should preferably be greater than atmosphericpressure, in order to prevent moisture from entering the refrigerationsystem.

The mechanical coefficient of performance is a measure which representsthe relative thermodynamic efficiency of a refrigerant in a specificrefrigeration cycle. This term is the ratio of the useful refrigerationpower to the mechanical energy consumed by the compressor.

The volume swept at the compressor reflects the refrigeration capacityof the refrigerant. The lower the volume of refrigerant necessary forobtaining a given refrigerating power, the greater its volumetriccapacity.

The results are collated in Table I.

Table I shows that the working conditions for refrigerants according tothe invention, of medium and low temperature type, appear to besufficiently close to those of R-22 to allow them to be used incompressors currently employing R-22.

In particular, VF2/R-134a binary refrigerants constitute a goodcompromise between the various performance criteria required forreplacing R-22 or R-502, and environmental protection criteria. Indeed,R-134a and 1,1-difluoroethylene do not contain chlorine and thereforehave an ODP equal to zero. Furthermore, these binary refrigerants havean HGWP which is less than that of R-134a and very much less than otherprior art refrigerants which contain R-23, R-143a or R-125. Althoughtest 2 shows the drawback of using R-134a in a refrigerating cycleoperating with a temperature at the start of evaporation of -30° C.,because of its insufficient vapour pressure which leads to the pressurein the evaporator being less than atmospheric pressure, test 3 showsthat a VF2 proportion of 5% by weight is sufficient, under theconditions examined, to achieve a greater pressure in the evaporatorthan atmospheric pressure. Furthermore, increasing quantities of VF2make it possible to enhance the refrigeration capacity, a refrigerationcapacity identical to that of R-22 being achieved when the VF2proportion is 20% by weight (tests 4 and 5).

Moreover, analysing Table I shows that, in a given refrigeration cycle,in comparison with known refrigerant mixtures consisting of twohydrofluoroalkanes, ternary refrigerants according to the invention, ofmedium and low temperature type, consisting of the same twohydrofluoroalkanes and VF2, lead to improved refrigeration capacity andpressure in the evaporator, without significantly affecting the othercharacteristic parameters of the refrigeration cycle.

Furthermore, comparing tests 11 and 12 shows that it is possible toreplace the R-23 contained in refrigerants of medium and low temperaturetype by VF2, which has an HGWP about 10,000 times less than that ofR-23, while retaining comparable refrigeration performance.

                  TABLE I                                                         ______________________________________                                             Refrigerant      T.sub.max                                                                            P.sub.ev       Vol.                              No.   (% by weight)     ° C.                                                                         R    COP   m.sup.3 /h                           ______________________________________                                        1*   R22              92.6   1.63 7.5  2.56 31                                2*           R134a            0.84   62.7                                                                         9.1                                                                               2.56                                                                              56                                3         VF2/R134a (5/95)                                                                                  1.02                                                                               10.1                                                                               2.35                                                                              48                                4         VF2/R134a (10/90)                                                                                79                                                                               1.2                                                                               10.4                                                                              2.23                                                                              41                                5         VF2/R134a (20/80)                                                                                87                                                                               1.75                                                                              9.7                                                                               2.15                                                                              31                                6       VF2/R134a/R125 (2/67/31)                                                                      64.7  1.23                                                                                8.8                                                                               2.41                                                                              42                                7         VF2/R134a/R125                                                                                    1.29.9                                                                              9.0                                                                               2.38                                                                              40                                            (3.5/66.5/30)                                                     8       VF2/R134a/R125 (4/71/25)                                                                      68.2  1.26                                                                                9.2                                                                               2.36                                                                              41                                9*       R134a/R32 (70/30)                                                                                 87.6                                                                           1.54                                                                                8.3                                                                               2.50                                                                              32                                10*     R134a/R32 (75/25)                                                                                  84.4                                                                           1.43                                                                                8.5                                                                               2.50                                                                              34                                11*   R23/R134a/R32 (2/67/31)                                                                          90.3                                                                               1.65                                                                                8.3                                                                               2.48                                                                              30                                12     VF2/R134a/R32 (2/67/31)                                                                         90.0                                                                               1.67                                                                                8.3                                                                               2.47                                                                              30                                13       VF2/R134a/R32                                                                                      1.720.6                                                                             8.3                                                                               2.45                                                                              29                                            (3.5/66.5/30)                                                     14     VF2/R134a/R32 (4/71/25)                                                                         88.2                                                                               1.63                                                                                8.5                                                                               2.44                                                                              31                                15*     R134a/R143a (70/30)                                                                              64.9                                                                             1.20                                                                                8.3                                                                               2.51                                                                              42                                16*     R134a/R143a (75/25)                                                                              64.8                                                                             1.13                                                                                8.4                                                                               2.51                                                                              44                                17       VF2/R134a/R143a                                                                                    1.307                                                                               8.4                                                                               2.45                                                                              40                                            (2/67/31)                                                         18       VF2/R134a/R143a                                                                                    1.365                                                                               8.5                                                                               2.41                                                                              38                                            (3.5/66.5/30)                                                     19       VF2/R134a/R143a                                                                                    1.314                                                                               8.7                                                                               2.40                                                                              39                                            (4/71/25)                                                         20     VF2/R134a/R290 (5/90/5)                                                                         71.7                                                                               1.10                                                                                9.6                                                                               2.37                                                                              45                                21     VF2/R134a/R290 (5/80/15)                                                                       70.2  1.23                                                                                8.7                                                                               2.41                                                                              42                                22*     R125/R143a (50/50)                                                                                55.2                                                                            2.16                                                                                6.8                                                                               2.33                                                                              29                                23       VF2/R125/R143a                                                                                     2.25.6                                                                              6.8                                                                               2.30                                                                              28                                            (2/50/48)                                                         24       VF2/R125/R143a                                                                                     2.40.8                                                                              6.8                                                                               2.27                                                                              26                                            (5/47.5/47.5)                                                     25     VF2/R125/R143a (5/50/45)                                                                       58.5  2.41                                                                                6.8                                                                               2.27                                                                              26                                26     VF2/R125/R152a (2/31/67)                                                                       77.0  1.09                                                                                8.7                                                                               2.51                                                                              44                                27       VF2/R125/R152a                                                                                     1.13.6                                                                              8.8                                                                               2.48                                                                              43                                            (3.5/30/66.5)                                                     28     VF2/R125/R152a (4/25/71)                                                                       80.2  1.10                                                                                8.9                                                                               2.49                                                                              44                                29*     R152a/R143a (70/30)                                                                              77.3                                                                             1.07                                                                                8.3                                                                               2.57                                                                              45                                30*     R152a/R143a (75/25)                                                                              77.9                                                                             1.02                                                                                8.4                                                                               2.58                                                                              46                                31       VF2/R152a/R143a                                                                                    1.151                                                                               8.3                                                                               2.53                                                                              42                                            (2/67/31)                                                         32       VF2/R152a/R143a                                                                                    1.196                                                                               8.4                                                                               2.50                                                                              41                                            (3.5/66.5/30)                                                     33       VF2/R152a/R143a                                                                                    1.158                                                                               8.6                                                                               2.50                                                                              42                                            (4/71/25)                                                         ______________________________________                                         *= Comparative examples                                                  

Example 2

A mixture of a VF2/R-134a refrigerant (10/90% by weight) with apolyester-type oil, marketed under the trademark TRITON® SEZ 32 by DEAMineralol AG and water was stored at 90° C. in various 300 ml stainlesssteel cylinders. Some of the cylinders furthermore contained a sample ofa molecular sieve (UOP XH9) or a copper or ordinary steel test-piece.The cylinders were kept under these conditions for about one month. Nochemical degradation of the refrigerant, no polymerization of the VF2,and no corrosion of the metal test-pieces were observed.

Example 3

A VF2/R-134a refrigerant (5/95% by weight) was tested, according tostandard ISO 917, in a refrigeration machine equipped with an open-typecompressor, the swept volume of which is 19.6 m³ /h, with a water-cooledcondenser and with an evaporator in contact with the air. Theperformance of this refrigerant was compared with that of R-22 in astandard refrigeration cycle. At a mean evaporation temperature of-35.8° C., with the refrigerant according to the invention, incomparison with R-22, a temperature 27.9° C. lower at the end ofcompression, a 9% higher compression ratio and a 13% lower electricalCOP were obtained.

Example 4

The composition of the VF2 and R-23 azeotrope was estimated by measuringthe equilibrium composition of the liquid phase (X) and of the vapourphase (Y) for various mixtures of VF2 and R-23, which were kept atconstant temperature. The equilibrium pressure was also measured. Theresults obtained are collated in Table II.

Whereas for low R-23 proportions, the R-23 molar fraction in the gasphase is greater than the R-23 molar fraction in the liquid phase, theopposite is found with high R-23 proportions, demonstrating theexistence of an R-23 and VF2 azeotrope.

On the basis of these experimental results, it was estimated, using theSoave-Redlich-Kwong state equation and the Uniquac parameters for theconstituents of the mixture, that the composition consisting of 58 mol %of R-23 and 42 mol % of VF2 is azeotropic at a pressure of 15.1 bar, andthat this azeotropic composition has a boiling point of -19.5° C. At apressure of 15.1 bar, the compositions consisting essentially of 30 to90 mol % of R-23 and 70 to 10 mol % of VF2 have a boiling point of-19±0.5° C.

                  TABLE II                                                        ______________________________________                                        Temperature                                                                             Pressure     .sup.X R-23                                                                            .sup.Y R-23                                   (° C.)                                                                               (bar)          (mole fr.)                                                                           (mole fr.)                                ______________________________________                                        -15.1     15.5         0.067    0.085                                         -17.4              14.7                                                                                       0.120                                                                                  0.148                                -16.4              15.8                                                                                       0.279                                                                                  0.314                                -18.2              16.0                                                                                       0.381                                                                                  0.414                                -18.2              15.7                                                                                       0.596                                                                                  0.602                                -18.0              15.9                                                                                       0.720                                                                                  0.711                                -18.2              15.1                                                                                       0.795                                                                                  0.781                                -18.2              15.4                                                                                       0.883                                                                                  0.868                                ______________________________________                                    

Example 5

An analysis of the thermodynamic performance of several refrigerantsaccording to the invention, of very-low temperature type, was performedin similar fashion to Example 1. By way of comparison with knownrefrigerants, the same analysis was performed for R-13, R-13B1 and R-503(R-13 and R-23 mixture in proportions by weight of 59.9/40.1).

The parameters of the refrigeration cycle are characteristic of very-lowtemperature systems. The parameters kept constant are superheating fixedat 10 K (temperature difference of 10° C.), subcooling fixed at 5 K(temperature difference of 5° C.) and an isentropic efficiency of thecompressor fixed at 0.8. The temperatures at the start of evaporationand at the end of compression which were set are given in Table III.

The temperature at the end of compression (T_(max)), the pressure in theevaporator (P_(ev)), the compression ratio (R=pressure in thecondenser/pressure in the evaporator), the mechanical coefficient ofperformance (COP), the volumetric refrigeration capacity (q_(v)) and thevolume swept in the compressor (Vol) required to obtain a refrigerationpower of 10 kW were estimated.

The results are collated in Table III.

Table III shows that the working conditions for the refrigerantsaccording to the invention, of very-low temperature type, appear to besufficiently close to those of R-13, R-13B1 or R-503 to allow them to beused in compressors which currently employ these refrigerants.

                                      TABLE III                                   __________________________________________________________________________       Refrigerant                                                                           T.sub.evap                                                                        T.sub.cond                                                                       T.sub.max                                                                         P.sub.ev                                                                                q.sub.v                                                                            Vol                                      No.                                                                               (% by weight)                                                                            (° C.)                                                                    (° C.)                                                                   (° C.)                                                                     (bar)                                                                            R  COP                                                                              (kJ/m.sup.3)                                                                      (m.sup.3 /h)                             __________________________________________________________________________    1* R-503   -88 -30                                                                              40.5                                                                              1.05                                                                             11.36                                                                             1.88                                                                             724  49.7                                     2      VF2/R23 (60/40)                                                                      -88                                                                                          11.53                                                                           1.91                                                                              700                                                                                    51.4                              3*     R-13                                                                                                  3.41                                                                             1287                                                                                    28.0                              4      VF2/R-125                                                                                           5.92                                                                            3.35                                                                              816                                                                                    44.1                                      (50/50)                                                               5      VF2/R-32 (50/50)                                                                    -70                                                                                           5.92                                                                            3.49                                                                              786                                                                                    45.8                              6*     R=13B1                                                                                              12.086                                                                          1.77                                                                              579                                                                                    62.2                              7      VF2/R-125/R-32                                                                        -60                                                                                         13.790                                                                          1.71                                                                              772                                                                                    46.6                                      (33.3/33.3/33.3)                                                      __________________________________________________________________________     *= Comparative examples                                                  

What is claimed is:
 1. A refrigerant consisting of from 0.1% to 99.9% byweight of 1,1-difluoroethylene and from 99.9% to 0.1% by weight of atleast one hydrofluoroalkane of formula C_(a) H_(b) F_(c), with a aninteger equal to 1 or 2, b an integer from 1 to 4 and c an integer from2 to 5, the sum of b and c being equal to 2a+2.
 2. The refrigerantaccording to claim 1, in which the hydrofluoroalkane is selected fromthe group consisting of difluoromethane, trifluoromethane,1,1-difluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane,pentafluoroethane and mixtures thereof.
 3. The refrigerant according toclaim 2, in which the hydrofluoroalkane is selected from the groupconsisting of difluoromethane, 1,1-difluoroethane,1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, pentafluoroethane andmixtures thereof.
 4. The refrigerant according to claim 3, consistingof(a) 1,1-difluoroethylene; (b) 1,1,1,2-tetrafluoroethane and/orpentafluorethane; and optionally (c) difluoromethane and/or1,1,1-trifluoroethane and/or 1,1-difluoroethane.
 5. The refrigerantaccording to claim 4, wherein (b) consists of 1,1,1,2-tetrafluoroethane.6. The refrigerant according to claim 4, wherein (c) consists ofdifluoromethane.
 7. The refrigerant according to claim 3, consistingof:(a) 1,1-difluoroethylene; (b) 1,1-difluoroethane; and (c)difluoromethane and/or 1,1,1-trifluoroethane.
 8. The refrigerantaccording to claim 3, consisting of from 65 to 99% by weight ofhydrofluoroalkane and from 1 to 35% by weight of 1,1-difluoroethylene.9. The refrigerant according to claim 2, in which the hydrofluoroalkaneis selected from the group consisting of difluoromethane,trifluoromethane, 1,1,1-trifluoroethane, pentafluoroethane and mixturesthereof.
 10. The refrigerant according to claim 9, consisting of(a)1,1-difluoroethylene; and (b) difluoromethane and/or1,1,1-trifluoroethane and/or pentafluoroethane.
 11. The refrigerantaccording to claim 9, consisting of(a) 1,1-difluoroethylene; (b)trifluoromethane; and optionally (c) difluoromethane and/or1,1,1-trifluoroethane and/or pentafluoroethane.
 12. The refrigerantaccording to claim 11, consisting of 1,1-difluoroethylene andtrifluoromethane.
 13. The refrigerant according to claim 11, consistingof from 70 to 10% mol 1,1-difluoroethylene and and from 30 to 90% moltrifluoromethane to form an azeotrope or a pseudo-azeotrope which willboil at -19±0.5° C. at a pressure of 15.1 bar.
 14. The refrigerantaccording to claim 9, consisting of from 10 to 95% by weight ofhydrofluoroalkane(s) and from 5 to 90% by weight of1,1-difluoroethylene.
 15. A refrigerant composition consisting of arefrigerant according to claim 1 and at least one additive selected fromthe group consisting of lubricants, VF2 polymerization inhibitors,corrosion inhibitors, and 1,1-difluoroethylene stabilizers.
 16. Arefrigerant composition according to claim 15, including from 0.1 to 50%by weight of additive.
 17. The refrigerant according to claim 12,consisting of from 70 to 10% mol 1,1-difluoroethylene and and from 30 to90% mol trifluoromethane to form an azeotrope or a pseudo-azeotropewhich will boil at -19±0.5° C. at a pressure of 15.1 bar.
 18. In amethod of operating heat transfer equipment which makes use ofcompression, the step of utilizing a refrigerant consisting of from 0.1%to 99.9% by weight 1,1-difluoroethylene and from 99.9% to 0.1% by weightof at least one hydrofluoroalkane of formula C_(a) H_(b) F_(c), with aan integer equal to 1 or 2, b an integer from 1 to 4 and c an integerfrom 2 to 5, the sum of b and c being equal to 2a+2.
 19. In a method ofoperating heat transfer equipment which makes use of compression, thestep of utilizing a refrigerant composition consisting of a refrigerantaccording to claim 1 and at least one additive selected from the groupconsisting of lubricants, VF2 polymerization inhibitors, corrosioninhibitors, and 1,1-difluoroethylene stabilizers.